Volume 22: Mini Workshop
Tackling Phylogeny in Introductory
Biology Laboratories
Marianne Niedzlek-Feaver and
John W. Zimmerman
Marianne Niedzlek-Feaver
Box 7617 Zoology
North Carolina State University
Raleigh, NC 27695-7617
919-515-9051
Fax 919-515-7519
Email:[email protected]
John W. Zimmerman
Science Division
400 N. Bluff Blvd.
Mount St. Clare College
Clinton IA 52732
319-242-4257 x2230
Fax 319-242-2003.
Email:[email protected]
Marianne Niedzlek-Feaver is an Associate Professor of Zoology at North
Carolina State University, where she teaches general biology and evolution. She
received her BS and MS in Biology from the University of Illinois and her PhD in
Zoology from the University of Michigan.
John W. Zimmerman, PhD in Zoology, has been teaching undergraduate
introductory biology courses for 14 years. John received his Ph.D. from and has
taught at North Carolina State University. Currently he is the Chair of the Science
Division at Mount St. Clare College, Clinton, Iowa.
Reprinted From: Niedzlek-Feaver, M. and J. W. Zimmerman. 2000. Tackling phylogeny in introductory
biology laboratories. Pages 377-378, in Tested studies for laboratory teaching, Volume 22 (S. J. Karcher,
Editor). Proceedings of the 22nd Workshop/Conference of the Association for Biology Laboratory
Education (ABLE), 489 pages.
- Copyright policy: http://www.zoo.utoronto.ca/able/volumes/copyright.htm
Although the laboratory exercises in ABLE proceedings volumes have been tested and due consideration
has been given to safety, individuals performing these exercises must assume all responsibility for risk. The
Association for Biology Laboratory Education (ABLE) disclaims any liability with regards to safety in
connection with the use of the exercises in its proceedings volumes.
©2001 Marianne Niedzlek-Feaver and John W. Zimmerman
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Introduction
In looking over course evaluations, we have often found students rank traditional
phylogeny laboratories low. Students feel such labs are exercises in memorization for later
regurgitation of numerous facts about dead subjects often encased in cloudy specimen jars.
Students are frustrated because they feel they lack the background to truly appreciate the trends
and relationships inherent in the diversity before them. Even when a laboratory about taxonomy is
presented as the capstone experience, the amount of information that students traditionally must
assimilate is usually large and so adds to student dissatisfaction. More importantly, the activities
involved are often some of most passive, and so perceived uninteresting, in the course.
We have made an effort to make learning about phylogeny a more worthwhile if not a more
pleasant experience by disseminating the information over a number of laboratories and including
as much hands-on and other active learning experiences in our named “phylogeny” laboratory.
We feel we have been most successful, as this laboratory has become one of the student’s
favorites; consistently over the last five years ranked among the top three. In a laboratory schedule
that includes laboratories devoted to such timely and frankly more “sexy” activities such as DNA
fingerprinting, this is no small accomplishment.
Our introductory biology course is one that draws not only life science majors, but also
majors from commodity departments (such as animal science and nutrition) as well as allied
science departments such as chemistry, physics, and engineering. Although non-science majors
are discouraged from taking the course we also draw about 1/3 of our students from the humanities
and social sciences. The course is taught from an evolutionary perspective and evolutionary
theory is treated early, weeks two and three, in the course. The first three laboratories contain
natural selection activities in addition to more traditional topics such as enzyme activity. Material
on phylogeny is formally integrated into several laboratories, actually four of the twelve true
laboratories (14 meetings minus an introduction and student presentation period) in this one
semester introductory biology course.
For example, one third of the material presented in our Cells laboratory is a survey of the
five kingdoms for the “types” of cells found in each. It includes then a formal introduction to the
idea of kingdoms. Some discussion of the different schemes used (a two-kingdom system and one
involving domains) is also given in lecture. We emphasize differences among the kingdoms
students can see, for example, cell size in prokaryotes as opposed to eukaryotes, and cell
specialization in plant and animal cells. These types of differences are also addressed in lecture at
the same time. Our first inheritance laboratory (primarily concerned with mitosis and meiosis)
adds information on the differences in life cycles in three kingdoms, Fungi, Plantae and Animalia.
After the animal classification laboratory, a laboratory on development and reproduction treats
evolutionary trends in the plant kingdom.
The Animal Classification Laboratory
Our named phylogeny laboratory surveys the animal kingdom because students are most
familiar with common characteristics in this group. Our diverse audience also is interested in
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learning more details about this kingdom than other kingdoms. We list three objectives for this
laboratory.
1. To experience classification as a dynamic and worthwhile activity
2. To appreciate evolutionary trends in the animal kingdom
3. To become more familiar with invertebrates
To accomplish these objectives we provide activities in which students themselves
determine the characteristics to be used in assessing relationships. Students are also asked to rank
the relationship or tree of those possible that best fits the data they have generated. Given that we
restrict the possible characteristics (particularly with the more unfamiliar invertebrate phyla) to
those that students can readily observe in the laboratory, we have turned potentially passive
activities into interactive discovery experiences.
Activities
Students are first introduced to the general scheme they will use to assess relationships.
Students are to assume all characters initially have the same value. They are presented with four
imaginary “bugs” and a table similar to ones they will construct listing “characteristics” for these
creatures. Then they are introduced to all the possible relationships that could exist between these
four animals and how to represent them. An excerpt from the laboratory manual that covers this
introduction follows.
An Example
We have four groups of organisms labeled A, B, C, and D. First, we make a list of the
characteristics shared by at least two groups. Then we make a table using our four groups as
column headings and the different characteristics as rows. We fill in the table, indicating who has
what characteristic.
Characteristic
legs
head
eyes
tail
stripes
A.
B.
C
D
A
B
C
D
2
yes
2
yes
no
4
yes
no
no
yes
2
yes
2
yes
yes
0
no
no
no
yes
Figure 1. Characteristics of four related imaginary organisms.
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With four groups only two different relationships are possible:
Relationship One
Relationship Two
Pairs of groups may share more characteristics Three groups may share more in common with
in common than with other groups.
each other than with a fourth group.
Relationship One diagrammed
Relationship Two diagrammed
Figure 2. The two possible relationships that can exist when only four groups related in some way
are considered.
How would you determine which relationship was the more correct depiction of shared
characteristics? The simplest way is to choose the relationship scheme that explains the greatest
numbers of characteristics shared by at least two groups.
Let us assume we are dealing with Relationship One, which is two groups more related to
each other than to other groups and the two remaining groups are also more related to each other
than to the other groups. (But we don't know which groups are more related to which.) Let's
redraw that relationship One diagram, leaving room to note which characteristics are explained by
the depicted relationship. We'll place the number of the characteristics explained in circles drawn
where we have joined lines representing two groups.
Figure 3. Relationship One drawn with circles at junctions.
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Now let us explore which groups should be placed together. First we will try them as
listed, A & B, C & D. Then, we'll group A & C, B & D. Finally, we'll group A & D, B & C. For
each possibility, we will place the number of shared characteristics by the two in the circle joining
the two groups. Note our second grouping is the best representation of how similarities are
distributed among the four groups, at least for Relationship One.
A
B
Possibility one
C
D
A
1
1
C
Possibility two
B
D
4
3
Possibility three
D
B
C
A
0
2
Figure 4. The possibilities for Relationship One.
The same can be done for Relationship Two. However, there are 12 possible ways to
distribute four groups using Relationship Two. See the diagram below. Consult your laboratory
instructor if you do not understand how the 12 different groupings for Relationship Two were
derived.
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D
C
D
B
B
C
C
D
A
B
A
A
D
B
B
C
A
A
D
B
C
C
A
B
A
A
B
D
B
C
C
B
C
A
A
A
D
D
C
A
D
B
C
B
D
D
C
D
Figure 5. The possibilities for Relationship Two.
The Vertebrates
Students are then assigned four vertebrate classes to classify. In different semesters we
have used different classes and different numbers of classes, although any one group of students
only compares four classes so that they can explore all possible relationships. Most recently, this
laboratory has been used early in the schedule and the emphasis has been then on gaining
familiarity with invertebrate phyla. The vertebrate exercise has been shortened to be a class
exercise on gaining experience with the scheme to be used, and reviewing facts learned about
vertebrates in lecture before tackling the invertebrates. We then have assigned the whole class
AVES, AMPHIBIA, MAMMALIA and REPTILIA. Each group of students fills out the table,
which adds characteristics students can observe in the laboratory to those treated in lecture such as
mode of temperature regulation or the excretory product typifying the group. Some skeletal
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characteristics are used, because of their commonness in the fossil record. The major criteria are
that students can readily observe the characters in the material provided. The laboratory manual
contains a short description of all characteristics students routinely use.
Students discuss and then vote on which characteristics to use for the various vertebrate
classes. For example, since a variety of reptilian skulls are available to students, they need to
decide if the turtle skull, alligator skull, or model tuatara skull should represent the norm for the
class Reptilia. Or they need to decide if the way skull type is defined should take into
consideration that all three types of skull can be found in this class.
Skull type: In the vertebrate line, skulls have become less flat, and
additional "openings" to allow jaw muscles to pass through before
attaching to the top of the skull are found. This gives more room for
jaw muscles and allows for more jawbone elaboration. Vertebrates
are classified as:
anapsid: no additional opening in position indicated on lab table
displays, right behind eye openings;
synapsid: one additional opening in position indicated on lab table
displays;
diapsid: two additional openings in positions indicated on lab table
displays.
Because the openings have been modified in most extant species, the number is difficult to quantify. You may wish to
classify groups as having broad skulls with evidence of jaw muscle attachment sites in proper positions or flat skulls
with no evidence of attachment sites. One of the biggest problems in comparing groups is trying to determine "what
constitutes a meaningful characteristic". Just remember if you construct a characteristic, such as extra holes or none,
apply it the same way every time you assess relationships.
Figure 6. Example of a description given in the lab manual for a character.
This is a good time to discuss character weighting. Should one character, such as mode of
reproduction, be assigned a higher point value than another character such as skull type?
Laboratory instructors report lively debates among students concerning the relative importance of
different characters.
Each table (group of four students) is then assigned three trees or relationships of the 15
possible to examine (see Figures 3 and 4). They enter their numbers on a transparency for the
whole class so that the class can easily observe which relationship best fits the characters chosen.
Often I discuss in lecture any discrepancies noted among laboratory sections in judgment
regarding best relationship. It is not uncommon for one laboratory section to have determined that
amphibians and reptiles are more closely related to each other than they are to mammal and birds
(Relationship One) only to have another section determine that amphibians, birds and reptiles are
more closely related to one another than they are to mammals (Relationship Two).
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If time permits, often the laboratory instructor will let the students compare weighted with
unweighted relationships or use different character tables to build relationships to illustrate further
classification as a dynamic activity. When this laboratory is the last in the schedule, we often
devote more time to this section. We will allow different student groups to do different vertebrate
classes or we will allow each table to use different characters and different numbers of characters
to build their relationships. Each student group then has to justify their approach to the rest of the
students in that laboratory section. Recently we have placed references in the laboratories for
student use, so they can add and later discuss the validity of adding behavioral or ecological
characters.
Invertebrates
Once students are familiar with building all possible trees using four vertebrate classes, so
only a reasonable number of trees are possible, they apply the method to become more familiar
with invertebrate phyla. With the invertebrates they commonly use only those characters they can
observe in the laboratory. We do provide a demonstration using live material on locomotionary
trends in animals to introduce them to structures of importance. Typically, students would score
easily observed characteristics such as presence or absence of a coelom (judged by animal
“thickness”), presence or absence of a skeleton and type of skeleton (exo or endo) present, type of
symmetry observed, and presence or absence of appendages and whether appendages are jointed.
We also have CDs available that students can use for reference that supplement the living material
with animations of muscle and joint movement, and show different animals moving through
various media. Instructors encourage debate and exploration of reference material, although the
characters students can observe in specimens found on the laboratory table are emphasized.
Generally each group of students compares three different invertebrate phyla to Arthropoda. As
students fill out tables and trees they apply what they are learning from the demonstration and
specimens found on the laboratory tables. The hope is that students are left with an impression of
taxonomy as a dynamic and challenging discipline, subject to critical testing, as any other
discipline in biology.
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SOLUTION ONE: THE HYDROSTATIC SKELETON
This is probably the first type of skeleton utilized in locomotion. Annelid worms are excellent examples of
a hydrostatic skeleton in the form of a coelom in action. In earthworms, sheaths of longitudinal and circular muscles
surround the hydrostatic skeleton or coelom. When the longitudinals shorten a short fat animal is produced, when
the circulars contract, a long thin one.
Locomotion begins with a contraction of the circular
muscles in a limited region of the anterior end of the body.
This contraction passes backwards down the body as a
wave, each wave of circular contraction being followed by
a wave of contraction of the longitudinal muscle. At those
regions where the longitudinal muscle is contracting the
body surface bulges outwards and the setae are protruded.
At these points, the worm can exert a thrust against the
substratum. Where the circular muscle is contracting the
body becomes thinner, and the setae are withdrawn. Here
the segments extend forward, aided by the thrust from the
swollen regions. Thus the extension of the thinner parts of
the body can be translated into forward movement. Waves
of this sort can be used to drive the animal along and if, as
in earthworms, some form of anti-slip device is
incorporated into the design, considerable forward pressure
can be generated.
Placing the worm on a glass plate can show the
importance of the thrust against something like a burrow
wall and the anti-slip device. Although the hydroskeleton
again gives effective movement in a viscous media (a
burrow for earthworms, water for other organisms with
hydrostatic skeletons), it proves ineffective for true forward
locomotion on land.
Compare how your earthworm moves when placed in
the center of a metal pan lined with a 1/4 inch layer of
moist dirt and an unlined metal pan.
Figure 7. An excerpt from the demonstration on locomotionary trends in the animal kingdom.
Several diagrams have already defined the term coelom and setae for students
For More Information
Our institution holds in part the copyright on the laboratory manual and requires, for
considerations of legal liability, that we monitor who receives copies of our laboratory preps. We
will be happy to send a hard or electronic copy (Mac platforms-MS word 5 or 98) of the laboratory
as it appears in the lab manual and the accompanying lab notes (demonstration material, set-up
diagrams and a list of references used) to educators who email asking for such. We will assume
such correspondence is your indication that you will acknowledge North Carolina State University
and the authors as the source of any materials you use from this paper or the lab manual in your
work. You are free then to use the material as you see fit in your classrooms, as long as you do not
hold North Carolina State, or the authors liable for any damages incurred in the process of doing
so. Materials can only be sent to institutional addresses. Please submit your request to the
following email address: [email protected]
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Acknowledgements
The authors wish to thank Ms. Patricia Aune and Ms. Theresa Johansson for their
continuing contributions to making this laboratory exercise a success, especially their oversight
and planning regarding laboratory set-up. Mr. Wall Crumpler and Ms. Susan Mumford offered
suggestions regarding this manuscript.
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